The Sydney Harbour Tunnel has reopened after a power failure led to its closure in both directions for more than an hour and a half, causing massive traffic queues on Monday morning.

A power outage occurred just after 10am at substations at Crows Nest and North Sydney, with Ausgrid saying its crews had to carry out important safety checks at the tunnel before the power could be restored.

Motorists were diverted to the bridge and advised to use Victoria Road, Anzac Bridge or Ryde Bridge instead.

The Transport Management Centre advised the tunnel reopened just before midday, with heavy traffic across the city’s CBD with queues of more than three kilometres in each direction.